The present invention relates to a frequency selective plate which performs high transparency of radio waves and visible rays while mainly reflecting near-infrared rays of solar radiation.
Lately, a window pane coated with a conductive thin layer or covered with a film including a conductive thin layer has been practically used for the purpose of shielding solar radiation. If such a window pane is applied to multistoried buildings, the window pane reflects radio waves of TV frequency range to generate ghost image in TV screen and to degrade receiving satellite broadcasting waves through indoor antenna. Further, if such a pane is applied to windows of a residence or an automobile, this functions to degrade the performance of handy telephones and the gain of an antenna embedded in the window pane. In order to solve these problems, a glass plate coated by heat-reflecting film is employed to transmit part of visible rays and to decrease the reflection of radio waves. Further, Japanese Patent No. 2620456 discloses a method for preventing a radio wave trouble by dividing a length of conductive film parallel to a field direction of incident radio waves into 1/20 the wavelength of the radio wave.
However, the former method employing the high-transparent heat-reflecting film is not sufficient in heat-ray shielding performance although a glass plate made by the former method prevents the radio wave trouble by decreasing the reflection of radio waves. Further, a glass plate made by the latter method disclosed in Japanese Patent No. 2620456 reflects visible rays and near-infrared rays since the divided length of the film is greater than the wavelength of the visible ray and near-infrared ray. Therefore, although this glass plate ensures a frequency selective performance having a radio wave transmitting performance and a solar radiation shielding performance, this cannot ensure the transparency of visible rays. Additionally, in case of a large window employing a large-size glass plate such as a glass plate having 2 mxc3x973 m size, it is necessary to take a very long time for cutting a dielectric film into segments of 1/20 satellite broadcasting wavelength of about 25 mm by means of a yttrium-aluminium-garnet (YAG) laser.
It is therefore an object of the present invention to provide an improved frequency selective plate having a radio wave transparency, and more particularly to a frequency selective plate which decreases a reflectance of radio waves ranging frequency band of TV broadcasting, satellite broadcasting and handy phone and prevents radio wave interference noise while preferably ensuring solar shielding performance and visual lay transparency.
An aspect of the present invention resides in a frequency selective plate which has a radio wave transparent property and comprises a substrate and an Ag layer of being dispersed with Ag particles and of being coated on said substrate.
Another aspect of the present invention resides in a production method of a frequency selective plate which method comprises the steps of (a) forming an Ag continuous layer on a substrate and (b) varying the Ag continuous layer into an Ag layer dispersed with Ag particles.